JP2018070732A - Polyethylene-based crosslinked shrink film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shrink film which can be degassed and steam is removed during heat shrinkage, has through holes whose pore diameter does not become too large after heat shrinkage, and has excellent transparency after heat shrinkage. To do. The polyethylene-based crosslinked shrink film of the present invention contains at least one polyethylene-based film layer, and has a root mean square height (Rq) of at least one surface as measured by a white laser interferometer. It is 0 to 50.0 nm and is characterized by having a through hole. [Selection diagram] None

Description

  The present invention relates to a polyethylene-based crosslinked shrink film.

  The shrink film for packaging can quickly and tightly package multiple products at the same time, regardless of the shape and size of the package, and the resulting package has a beautiful appearance and exhibits a display effect. It is often used for packaging food, sundries, etc. because it increases the value of the product, keeps the contents hygienic, and facilitates visual quality confirmation.

  As a packaging method using such a shrink film for packaging, a method in which the film is heat-shrinked with hot air after the contents are primarily packaged with a little room, and a pillow shrink packaging is a typical example. It is an example. In this method, generally, a food or other packaged object stored in a container or tray is covered with a film in a cylindrical shape, and then a sealing wire is formed on the back surface of the packaged object by a center seal device such as a rotary roller type. And then heat-sealing both open ends of the tubular film to form a bag, heat treatment with hot air in a box called a shrink tunnel, This is heated and shrunk while air is deaerated. In addition to the above, this pillow shrink packaging includes a three-sided seal and a method of heating a four-side sealed bag-like film.

  As a main example of a package to be subjected to pillow shrink wrapping using a film provided with such a hole, a heat-resistant container such as made of polystyrene with a lunch box or a side dish containing a side dish or made of polypropylene (PP) with filler, Examples include trays made of expanded polystyrene, PP, paper, etc. without lids that contain meat and fish. In each case, wrap the containers and trays with plenty of room, and then blow hot air. A method of shrinking is mentioned.

  By the way, in packaging of a packaged object such as a lunch box or a side dish, reheating in a microwave oven is often performed after packaging, and if the container is highly sealed, the air inside expands and the fitting part is disengaged. Since the container is easily deformed by heat and pressure, the juice and sauces of the ingredients in the container easily flow out of the container, and the outside of the container is easily contaminated. Therefore, in order to release the pressure at the time of range heating moderately, the top surface 1-2 places of the container lid are punched into a U shape as a steam port.

On the other hand, if the hole provided in the shrink wrapping is too large, small insects such as fleas may invade from the hole during the distribution of lunch boxes and prepared dishes, and there is a risk of contamination such as entry into the interior from the steam port. There is.
Examples of this include cut vegetable packaging in which vegetables such as radish and Chinese cabbage cut into 1/2 or 1/4 are directly packaged with a film, and the problem of foreign matter contamination is the same. Therefore, it is necessary to prevent insects from entering.
Patent Document 1 discloses a shrink film.

JP, 2014-234190, A

  The shrink film described in Patent Document 1 has a large hole, and there is a problem that a hole diameter becomes large when packaging by heat shrinkage and foreign matters are mixed.

  Therefore, the present invention provides a shrinkable film that can be degassed and degassed during heat shrinkage, has a through-hole that does not become too large after heat shrinkage, and has excellent transparency after heat shrinkage. Objective.

That is, the present invention is as follows.
[1]
It includes at least one polyethylene-based film layer, and has a root mean square height (Rq) of at least one surface measured by a white laser interferometer of 10.0 to 50.0 nm and having a through hole. A polyethylene-based cross-linked shrink film.

[2]
The polyethylene type crosslinked film according to [1], wherein the through hole has a hole diameter of 1 to 500 μm.

[3]
The polyethylene-based crosslinked film according to [1] or [2], which has 100 to 3000 through-holes per 10 cm ² .

[4]
A bento / prepared food package, which is packaged with the polyethylene-based crosslinked shrink film according to any one of [1] to [3].

[5]
A cut vegetable packaging packaged with the polyethylene-based crosslinked shrink film according to any one of [1] to [3].

  Since the polyethylene cross-linked shrink film of the present invention has the above-described configuration, it can be degassed and discharged with steam at the time of heat shrinkage, has a through hole whose diameter does not become too large after heat shrinkage, and is also transparent after heat shrinkage. Excellent.

FIG. 1 is a schematic plan view showing an example of a method of providing a through hole at the intersection of two notches.

  Hereinafter, a form for carrying out the polyethylene cross-linked shrink film, lunch box / prepared food package and cut vegetable package of the present invention (hereinafter simply referred to as “this embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

[Polyethylene cross-linked shrink film]
The polyethylene cross-linked shrink film of this embodiment includes at least one polyethylene-based film layer, and the root mean square height (Rq) of at least one surface measured by a white laser interferometer is 10.0 to 50. It is 0 nm and has a through hole.

  The polyethylene cross-linked shrink film of this embodiment may be a single-layer film of a polyethylene-based film layer or a laminated film including at least one polyethylene-based film layer. When the polyethylene cross-linked shrink film of the present embodiment is a laminated film, it may be a laminated film of the same or different polyethylene film layer, or may be a laminated film including other layers other than the polyethylene film layer. .

(Polyethylene film layer)
Examples of polyethylene constituting the polyethylene film layer include low-density polyethylene such as high-pressure low-density polyethylene and linear low-density polyethylene, and polyethylene containing ethylene as a structural unit such as an ethylene-α-olefin copolymer. It is done. The polyethylene film layer may be a layer containing one kind of polyethylene or a layer containing two or more kinds of polyethylene.
In addition, in the said polyethylene-type film layer, in the range which does not impair the effect of this invention, other resin, such as a propylene-type resin, a styrene resin, a butene resin; Glycerin fatty acid ester, polyglycerol fatty acid ester, sorbitan fatty acid ester, Antifogging agents such as ethylene oxide adducts; Plasticizers such as liquid paraffin; Lubricants such as natural silica, synthetic silica, saturated fatty acid amide, unsaturated fatty acid amide, and talc; Antiblocking agent; Antistatic agent; Antioxidant; May be included.

  The high-pressure method low-density polyethylene is a low-density polyethylene produced by a high-pressure method, and is a polyethylene-based resin in which repeating units of ethylene are randomly linked with branches and long-chain branches.

The density of the high-pressure low-density polyethylene is preferably 0.915 to 0.930 g / cm ³ , more preferably 0.917 to 0.925 g / cm ³ from the viewpoints of film flexibility and transparency. It is. In this specification, the density means a value measured according to JIS K 6922.

  The melt flow rate (MFR) of the high-pressure method low-density polyethylene is preferably 0.2 to 2.0 g / 10 minutes, more preferably 0.2 to 2.0% from the viewpoint of stability during extrusion or stretching. 1.5 g / 10 min. In the present specification, MFR means a value measured according to JIS K 7210, 190 ° C., 2.16 kg).

  A generally known method can be used as a method for producing the high-pressure low-density polyethylene. In general, high-pressure low-density polyethylene is produced by polymerizing ethylene and α-olefin in an autoclave or tube reactor in the presence of a free radical generator such as peroxide under high temperature and high pressure of 100 to 300 ° C and 100 to 350 MPa. can do.

The density of the linear low-density polyethylene is preferably 0.910 to 0.930 g / cm ³ , more preferably 0.910 to 0.926 g / cm ³ from the viewpoint of flexibility and transparency of the film. ³ .

  The melt flow rate (MFR) of the linear low density polyethylene is preferably 1.0 to 3.0 g / 10 minutes, more preferably 1.2 from the viewpoint of stability during extrusion and stretching. ~ 2.5 g / 10 min.

  Examples of the ethylene-α-olefin copolymer include a copolymer of ethylene and at least one monomer selected from α-olefins having 3 to 18 carbon atoms. Examples of the α-olefin having 3 to 18 carbon atoms include propylene, butene-1, pentene-1, 4-methyl-pentene-1, hexene-1, octene-1, decene-1, dodecene-1, and the like. It is done. Among these, an ethylene-octene-1 copolymer is preferable from the viewpoint of tensile strength and tear strength.

The density of the ethylene-α-olefin copolymer is preferably 0.865 to 0.925 g / cm ³ , more preferably 0.870 to 0.922 g / cm, from the viewpoint of flexibility and transparency. ³ .

  The melt flow rate (MFR) of the ethylene-α-olefin copolymer is preferably 0.5 to 4.0 g / 10 minutes, more preferably 0, from the viewpoint of stability during extrusion or stretching. .8 to 2.5 g / 10 min.

Although the polymerization catalyst used when manufacturing the said ethylene-alpha-olefin copolymer is not specifically limited, For example, a multi-site catalyst, a single site catalyst, etc. are mentioned.
The ethylene-α-olefin copolymers may be used singly or as a mixture of two or more densities or different comonomer types.

  The polyethylene-based crosslinked shrink film of the present embodiment is preferably a laminated film of the polyethylene-based film layer. Among these, from the viewpoint of easy adjustment of the root mean square height of the surface, at least one surface is preferably a polyethylene film layer, and both surfaces are preferably polyethylene film layers.

(Other layers)
Although it will not specifically limit as said other layer if it is a layer which does not impair the effect of this invention, For example, the film layer etc. which contain the said other resin are mentioned.

(Through hole)
The polyethylene type crosslinked shrink film of the present embodiment has a through hole.
The diameter of the through hole is preferably 1 to 500 μm, more preferably 10 to 400 μm, from the viewpoint of more reliably preventing the entry of small insects even after heat shrinkage.
In addition, the hole diameter of a through-hole can be measured by the method as described in the below-mentioned Example. The hole diameter of each through hole refers to the largest diameter among the diameters of circles circumscribing the portion forming each through hole.

The density of the above-mentioned through holes is good for air escape during heat shrinkage, the appearance of the shrinkage finish is good, air escape is moderate after packaging, and wrinkles are less likely to occur. From the viewpoint that it is easy to release the internal pressure moderately when heating with a range or the like, the number is preferably 100 to 3000, more preferably 150 per 10 cm ² of the surface of the polyethylene-based crosslinked shrink film of the present embodiment. ~ 1500.

  The minimum interval between the through holes is preferably 1 to 10 mm, more preferably 1.5 to 8 mm, and further preferably 2 to 5 mm. In addition, the minimum space | interval between through-holes means the minimum value among the distances between the arbitrary two through-holes on a polyethylene type crosslinked shrink film.

When the polyethylene-based crosslinked shrink film of the present embodiment is a laminated film, the surface mean square root height is more easily adjusted, and from the viewpoint of further excellent transparency, the surface layer contains an ethylene-α olefin copolymer. Is preferred.
The mass ratio of the ethylene-α-olefin copolymer in the surface layer is preferably 70 to 100% by mass and more preferably based on the total mass (100% by mass) of the surface layer from the viewpoint of further excellent transparency. Is 80 to 100% by mass, more preferably 100% by mass.

As a polyethylene type crosslinked shrink film of this embodiment, the film of at least 3 layers which has the intermediate | middle layer which has the following (a) as a main component, and the surface layer which has the following (b) as a main component may be sufficient, for example ( a) Low density polyethylene (A) having a long chain branch produced by a high pressure method having a density of 0.915 to 0.930 g / cm ³ and an MFR of 0.2 to 2.0 g / 10 min, a density The resin composition which consists of 10-50 weight part of 0.865-0.925g / cm < ³ >, ethylene-alpha olefin copolymer (B) which is MFR0.5-4.0g / 10min.
(B) A linear low density polyethylene (C) having a density of 0.910 to 0.930 g / cm ³ and an MFR of 1.0 to 3.0 g / 10 min.
As a layer structure of the polyethylene type crosslinked shrink film of this embodiment, for example, a layer structure of at least three layers or more is mentioned, and a three-layer structure of (b) / (a) / (b), (b) / (a ) And (b) mixed layer / (a) / (a) mixed layer (b) / (b), (b) / (a) / (a) mixed with (b) 5 layer constitutions such as layer / (a) / (b).
Among these, a layer configuration in which a layer in which (a) and (b) are mixed is suitable because it is easy to adjust various physical properties and mix and use recycled resins. The mixing ratio in the layer in which (a) and (b) are mixed is not particularly limited.

  The polyethylene-based crosslinked shrink film of the present embodiment may be, for example, a laminated film in which three layers of polyethylene-based films are laminated. Specifically, a polyethylene-based film containing an ethylene-α olefin copolymer (preferably Is a polyethylene film comprising only an ethylene-α olefin copolymer) / a polyethylene film comprising an ethylene-α olefin copolymer (preferably a polyethylene film comprising only an ethylene-α olefin copolymer) or polyethylene. Polyethylene film containing (preferably a polyethylene film comprising an ethylene-α olefin copolymer and high-pressure low-density polyethylene) / Polyethylene film containing an ethylene-α olefin copolymer (preferably an ethylene-α olefin copolymer) Heavy Body polyethylene film comprising only), and three-layer laminated films of.

(Production method)
Examples of the method for producing the polyethylene-based crosslinked shrink film of the present embodiment include a method of producing a heat-shrinkable film (shrink film) such as a single layer film or a multilayer film, and subjecting the heat-shrinkable film to perforation treatment. Can be mentioned.

-Production of heat-shrinkable film-
Examples of the method for producing the heat-shrinkable film include the following methods.
A film produced using the above resin may be stretched by a known longitudinal and transverse simultaneous biaxial stretching method. The stretching ratio is preferably 3 to 6 times in both length and width. If it is less than 3 times, the modulus is lowered and heat resistance failure due to large swelling of the bag-making film in the shrink tunnel, and the vertical streak-like appearance defect seen after shrink wrapping occur, which is not preferable. When it exceeds, tear strength will fall and it is not preferable.
Hereinafter, the case of three-layer laminated annular film-forming stretching will be described as an example.
First, the resin or resin composition constituting the intermediate layer and the surface layer is melt-kneaded by three extruders, co-extruded in a ring form from a three-layer annular die, and then rapidly cooled and solidified without being stretched to form a tubular unstretched film Is made. Subsequently, an electron beam irradiation apparatus irradiates an electron beam to both surfaces of a tubular unstretched film on the irradiation conditions of 20-60 kGy, and produces a crosslinked tubular unstretched film. The obtained crosslinked tubular unstretched film is supplied to a tubular stretching apparatus, and is in a highly orientable temperature range, for example, at a temperature lower than 10 ° C. below the melting point of the intermediate layer resin, preferably below 15 ° C. below the melting point. By applying gas pressure to the inside of the tube at a low temperature and expanding and stretching, simultaneous biaxial orientation is caused at a stretching ratio of 3 to 6 in both length and width. The film taken out from the stretching apparatus can be annealed as desired, and the natural shrinkage during storage can be suppressed by this annealing.

  Although it does not specifically limit as another manufacturing method of the said heat-shrinkable film, You may manufacture as a single layer film by single layer extrusion, may manufacture as a multilayer film by co-extrusion, and each layer is separated separately. It may be formed and then laminated to produce a multilayer film. Especially, when manufacturing a multilayer film, it is preferable to manufacture by coextrusion by a melt extrusion method. For example, the method which melt | dissolves resin or resin composition which comprises each layer with each extruder, and coextrudes with a multilayer circular die etc. is mentioned.

The polyethylene-based crosslinked shrink film of the present embodiment is a film subjected to crosslinking treatment from the viewpoint that heat resistance is imparted and that the film can be stably stretched even with a thickness of about 5 to 15 μm. It is preferable.
A gel fraction is used as a measure of the degree of crosslinking. Here, the gel fraction is the ratio of the portion that remains without being dissolved after immersing the polyethylene-based crosslinked shrink film in boiling paraxylene for 12 hours, and is represented by the following formula.
Gel fraction (% by mass) = (mass of polyethylene-based crosslinked shrink film after immersion / mass of polyethylene-based crosslinked shrink film before immersion) × 100
The gel fraction of the polyethylene-based crosslinked shrink film of the present embodiment is preferably 5 to 40% by mass and more preferably 10 to 35% by mass from the viewpoint of film stretchability and heat resistance.

  Examples of the crosslinking treatment include irradiation with energy rays such as electron beams, ultraviolet rays, X rays, α rays, and γ rays. The preferable irradiation dose range for the crosslinking treatment is preferably 10 to 150 kGy from the viewpoint that the root mean square height of the surface can be adjusted to an appropriate range, and 20 to 120 kGy from the viewpoint of heat sealability and stretching stability. Is more preferable.

As a polyethylene type crosslinked shrink film of this embodiment, the film which gave the extending | stretching process is preferable. Specifically, the unstretched heat-shrinkable film is subjected to a crosslinking treatment to enable a high degree of orientation (preferably a temperature lower than the melting point of the resin constituting the intermediate layer by 10 ° C. or less, more preferably an intermediate layer). It is preferable to perform sequential biaxial stretching or simultaneous biaxial stretching of 3 to 6 times in the flow direction and / or the width direction at a temperature lower than the melting point of the constituent resin by 15 ° C. or less. Among these, sequential biaxial stretching is preferable from the viewpoint that a through-hole having an appropriate hole diameter is easily obtained. The stretching method is particularly preferably a double bubble inflation method, and this method is suitable for stretching a thin film of about 10 μm.
In this specification, the flow direction (MD direction) refers to the extrusion direction during film formation, and the width direction (TD direction) refers to the direction orthogonal to the extrusion direction on the film surface.

Specific examples of the production method for forming a film by the double bubble inflation method include the following methods.
The resin composition constituting each layer is melt-extruded using an extruder, and the layers are sequentially joined together in an annular die or joined once in the annular die to obtain a multi-layered tube-shaped unstretched original fabric . At this time, one extruder may be used per layer, or it may be divided into two or more by the time the resin composition flows from one extruder into the annular die. . This is rapidly cooled and solidified, guided into a stretching machine, and the heating temperature at the stretching start point is set in the range from the melting point of the resin composition to −10 ° C. to the melting point + 40 ° C. Injection is performed, and stretching is performed 4.0 times or more in the flow direction and the width direction, respectively.
The upper limit of the stretching ratio is preferably 12.0 times or less from the viewpoint of stretching stability. By stretching at a temperature equal to or higher than the melting point of the resin composition constituting each layer, high-magnification stretching can be performed, and a film having a high shrinkage rate can be obtained.

The polyethylene-based crosslinked shrink film of this embodiment preferably has a shrinkage rate of 100 ° C. of 1% or more and less than 30%, and a shrinkage rate of 110 ° C. of 30% or more and 95% or less. Further, from the viewpoint of improving the packaging finish, the shrinkage rate at 140 ° C. is preferably 68% or more and 95% or less.
Here, the shrinkage rate is an average value of the shrinkage rate in the flow direction and the shrinkage rate in the width direction of the film.
The shrinkage rate was measured by measuring the length in the flow direction and width direction of the film before heating (before shrinkage) and after heating for 30 minutes in the hot air dryer at each temperature (after shrinkage), and using the measured lengths. The shrinkage rate in each direction can be calculated by the following formula, and the average of the shrinkage rate in the flow direction and the shrinkage rate in the width direction can be obtained.
Shrinkage rate (%) = {(length before shrinkage−length after shrinkage) / length before shrinkage} × 100

  When the shrinkage rate of the polyethylene-based crosslinked film of this embodiment is in the above range, the packaged container is less likely to be deformed when the packaging container heat-shrink-wrapped with the polyethylene-based crosslinked shrink film is reheated by microwave heating or the like. Moreover, it becomes easy to carry out low temperature packaging. Low temperature packaging here includes lowering the set temperature of the shrink tunnel during heat shrink packaging, shortening the transit time in the shrink tunnel, keeping the seal line away from the package, etc., and suppressing shrinkage wrinkles. it can. In addition, when pillow-wrapping, if the heat-shrinkable film is easy to tear in the flow direction, when temporarily wrapping the package body with sharp corners with the film, the film will tear from the contact part with the package body, and the tear May propagate to the vicinity of the feeding portion of the film. In such a case, it is necessary to start the packaging operation from the beginning, resulting in a large loss.

  The obtained polyethylene cross-linked shrink film can be slit into a predetermined size and used for packaging.

The polyethylene-based crosslinked shrink film of the present embodiment may be subjected to surface treatment such as corona treatment, ozone treatment, flame treatment and the like from the viewpoint of becoming a film suitable for printing applications. The surface treatment may be performed either before or after the drilling process.
When performing the printing process, 0.5 to 5.0% by mass of glycerin fatty acid ester or the like is added to the resin composition constituting the surface layer to be the printing surface, and after the film is formed, the printing surface is subjected to corona treatment. It is preferable to perform the printing process after the operation. From the viewpoint of antistatic properties and prevention of ink peeling, the addition amount of glycerin fatty acid ester and the like is more preferably 0.8 to 3.0% by mass with respect to the resin composition constituting the surface layer.

  Furthermore, in the polyethylene-based crosslinked shrink film of the present embodiment, a tackifying resin such as Alcon (trademark), Clearon (registered trademark), or Imabe (registered trademark) or a petroleum-based resin is used as a plasticizer in any of the constituent layers. May be included. As content of the said plasticizer, if it is 0.1-10 mass% with respect to the resin composition which comprises each layer, contractility and transparency may improve.

-Porosity treatment-
A method for providing a through hole in the heat-shrinkable film is not particularly limited. For example, a method of providing a through hole by a needle-like protrusion, a cut A that does not penetrate the film is provided on one surface, and a film is provided on the other surface. And a method of providing a notch B that does not pass through the surface and providing a through hole at the intersection of the two notches. Above all, it is a hole diameter that can prevent the entry of small insects even after heat shrinkage, the air escape during heat shrinkage is good, the appearance of the shrinkage finish is good, the air escape is moderate, and wrinkles are not likely to occur From the viewpoint of providing a more stable through hole, a method of providing a through hole at the intersection of two notches is preferable.

FIG. 1 is a schematic plan view showing an example of a method of providing a through hole at the intersection of two notches. A plurality of cuts A <b> 2 are provided on one surface of the film 1, and a plurality of cuts B <b> 3 are provided on the other surface of the film 1. The cuts A2 and B3 may be provided continuously (for example, across the film) over the entire width of the film, or a plurality of cuts may be provided intermittently as shown in FIG. .
A through hole 4 is provided at the intersection of the cut A2 and the cut B3. The through holes 4 may be provided at all intersections between the notches A2 and B3, or may be provided at a part thereof.
The cut A2 extends in a direction inclined by an angle φ1 with respect to the tear propagation direction TTD. Further, the cut B3 extends in a direction inclined by an angle φ2 with respect to the tear propagation direction TTD. Here, it is preferable that (phi) 1 and (phi) 2 are 30-60 degrees. φ1 and φ2 may be the same angle or different angles. The total of φ1 and φ2 may be 90 °.

The number of the cuts A and the number of the cuts B are not particularly limited, but are preferably two or more. Moreover, each notch A may be parallel and does not need to be parallel. Each notch B may be parallel and may not be parallel. Especially, it is preferable that each notch A and each notch B are parallel from a viewpoint of the ease of manufacture and cost.
The interval between the cuts A (pitch, the interval Q2 between adjacent cuts A2) and the interval between the cuts B (pitch, interval Q1 between adjacent cuts B3) can further prevent the through-holes from being excessively enlarged during heat shrink packaging. From the viewpoint, it is preferably 0.2 mm or more, and more preferably 0.5 mm or more. The notch interval refers to the length of the shortest perpendicular line among the perpendicular lines from one notch to the other notch. For example, in FIG. 1 in which the cuts A are provided in parallel, the shortest distance Q2 in the perpendicular direction DD1 with respect to each cut A2. In FIG. 1 in which the cuts B are provided in parallel, the shortest distance Q1 in the perpendicular direction DD2 with respect to each cut B3.

  For example, the lengths of the cut A and the cut B are preferably 2 to 100% and more preferably 5 to 80%, respectively, with respect to the entire width of the film. When there are a plurality of cuts, the lengths of the cuts may be different from each other or all may be the same length.

  The depth of the cut A and the cut B is not particularly limited as long as the cut does not penetrate the film.

As a method of forming the cut A and the cut B, for example, the first blade from the one surface side of the film and the second blade from the other surface side (back surface side) of the film to the film surface, respectively. A method of forming a cut by applying perpendicularly to the surface is preferable.
At this time, if the tear propagation direction is 0 °, the first blade is rotated 30-30 ° clockwise on the film surface, and the second blade is rotated 30-60 ° counterclockwise. It is preferable that the blade is applied so as to sandwich the film to form the cut and the through hole. Specifically, the first blade in a direction that forms an angle φ1 of 30 to 60 ° with respect to the tear propagation direction TTD, and the second blade in a direction that forms an angle φ2 of 30 to 60 ° with respect to the tear propagation direction TTD. Is applied so that the film is sandwiched between the first blade and the second blade, and the first blade and the second blade are in contact with the first blade and the second blade. It is preferable to form each hole (FIG. 1).

  Alternatively, two or more films may be stacked and punched.

The tear propagation direction is a film having a width of 50 mm, a length of 64.5 mm, and a thickness of 7 to 20 μm (film before drilling), a tear tester (manufactured by Toyo Seiki Co., Ltd., trade name “light load tear tester”). The film MD direction and the film TD direction are tested under the condition of the measurement range of 50 g. The film tear direction propagates in the film MD direction tear test, and the film tear direction propagates in the film TD direction tear test. Or the intermediate direction between the direction in which the film tear propagated in the tear test in the film MD direction and the direction in which the film tear propagated in the tear test in the film TD direction.
Specifically, the tear propagation direction can be determined by the following criteria, for example.
1. In the tear test in the MD direction and the tear test in the TD direction, when the direction in which the tear of the film propagates goes straight with respect to the MD direction or the TD direction, the tear propagation direction is the MD direction or the TD direction.
2. When the tear of the film propagates in a different direction without going straight in the tear test in the MD direction, and the tear tear propagates in the straight direction in the tear test in the TD direction, the tear propagation direction may be the different direction or the straight forward This is the direction in which the tears propagated.
3. If the vehicle does not go straight in either the MD or TD direction, it is the intermediate direction.

When the cut A is formed by rotating 0 to 29 ° with respect to the tear propagation direction, since the direction of the cut A is close to the tear propagation direction, the through hole tends to spread in the MD direction, and after heat shrink packaging The diameter of the through-hole tends to increase.
When the cut A is formed by rotating 61 to 89 ° with respect to the tear propagation direction, the direction of the cut A is close to the TD direction and easily spreads in the TD direction. The hole diameter tends to be large. Further, when the cut A and the cut B are provided at right angles, the direction of the cut B is close to the MD direction, and the hole diameter of the through hole after heat shrink wrapping tends to expand in the MD direction, which is not preferable.

(Physical properties)
It describes about the physical property of the polyethylene type crosslinked shrink film of this embodiment.

The polyethylene-based crosslinked shrink film of the present embodiment has a moderate roughness on the surface, can reduce troubles due to catching in a wide variety of drilling processes, and can stably provide through-holes with an appropriate hole diameter. Therefore, it has practical characteristics such as deaeration at the time of shrink wrapping and steam removal at the time of heating in a microwave oven, and it is very unlikely that foreign matter such as small insects enter from the through-hole after packaging, and shrink wrap From the viewpoint of excellent transparency later, the root mean square height (Rq) of at least one surface is 10.0 to 50.0 nm, preferably 12 to 45 nm.
In addition, a root mean square height can be measured by the method as described in the below-mentioned Example.
The root mean square height is, for example, the type and manufacturing method of the film forming the surface layer, the film crosslinking conditions, the stretching conditions, the cooling conditions after stretching, the relaxation treatment conditions for imparting dimensional stability of the film, etc. Can be adjusted.

  The thickness of the polyethylene-based crosslinked shrink film of the present embodiment is preferably 6 to 12 μm, more preferably 7 from the viewpoint of practical film strength and resource saving required when an automatic packaging machine is used. ~ 11μm

  When the polyethylene type crosslinked shrink film of this embodiment is a laminated film, the thickness ratio of the intermediate layer other than the surface layer is 40 to 80% with respect to the total thickness from the viewpoint of the appearance after shrink wrapping and the efficiency of shrink wrapping It is preferable that it is 50 to 70%.

  The polyethylene-based cross-linked shrink film of the present embodiment can be suitably used for a bento box and side dish shrinkage packaging application. In particular, in the case of heating in a microwave oven or the like before opening the lunch box / prepared food wrapped with the polyethylene-based crosslinked shrink film of the present embodiment, the steam escapes from the through-hole expanded by heating, and the container is deformed. In addition, small insects are less likely to enter after packaging.

  The polyethylene type cross-linked shrink film of the present embodiment can be suitably used for shrink wrapping of cut vegetables. In particular, for irregularly shaped items that have been cut into ½ or ¼ of radish and Chinese cabbage, through-hole scratches are attached to a wide area of the film, so that air during contraction can be easily removed, so there is no corner residue. Good packaging finish. Moreover, since the through-hole does not expand too much at the time of packaging, it is difficult for small insects to enter.

  Moreover, the lunch box and side dish package of this invention are packaged with the polyethylene type crosslinked shrink film of this embodiment. Moreover, the cut vegetable packaging body of this invention is packaged with the polyethylene type crosslinked shrink film of this embodiment.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

The measurement methods used in the examples and comparative examples are described below.
(Root mean square height (Rq))
Using the white laser interferometer (product name “NEW VIEW 8000”, manufactured by Zygo), the surface of the surface layer of the polyethylene-based crosslinked shrink film obtained in the examples and comparative examples was attached, and scanning was performed. The root mean square height (nm) was measured.
The measurement was performed in the range of 0.3 mm in the MD direction and 0.3 mm in the TD direction on one surface, and the surface excluding foreign matter such as unmelted material, carbon and dust, cuts, and through holes was targeted. .

(Diameter of through hole, density of through hole)
The hole diameter of the through-hole of the polyethylene type crosslinked shrink film obtained by the Example and the comparative example, and the density of the through-hole were measured. Incidentally, the diameter of the through-hole ([mu] m), and the density of the through holes (pieces / 10 cm ²⁾ was determined for any range of 10 cm ² of polyethylene crosslinked shrink film surface. Moreover, the average value of all the through-holes was made into the hole diameter of a through-hole.

(Haze after heat shrink)
Using the polyethylene-based cross-linked shrink film obtained in the examples and comparative examples, a pillow wrapping machine FW3451AαV (manufactured by Fujikikai Co., Ltd.) was used to wrap ES-Xinjiang (manufactured by FP Corporation) with 200 g of cooked rice. Shrink in a shrink tunnel set at 145 ° C. to obtain a tight package.
The haze (%) of the polyethylene-based crosslinked shrink film after packaging was measured according to a haze meter (NDH7000, manufactured by Nippon Denshoku Industries Co., Ltd.) ASTM D-1003.

(Maximum pore size after heat shrinkage)
Using the polyethylene-based cross-linked shrink film obtained in the examples and comparative examples, a pillow wrapping machine FW3451AαV (manufactured by Fujikikai Co., Ltd.) was used to wrap ES-Xinjiang (manufactured by FP Corporation) with 200 g of cooked rice. Shrink in a shrink tunnel set at 145 ° C. to obtain a tight package.
About the range of 30 mm of MD directions and 30 mm of TD directions of the polyethylene-type crosslinked shrink film after packaging, the hole diameter of the through-hole was measured, and the maximum value was made into the maximum hole diameter (micrometer).

(raw materials)
LL1: ethylene-octene-1 copolymer, density 0.920 g / cm ³ , MFR 1.0 g / 10 min,
LL2: ethylene-octene-1 copolymer, density 0.905 g / cm ³ , MFR 0.8 g / 10 min LD1: high pressure method low density polyethylene, density 0.920 g / cm ³ , MFR 0.3 g / 10 min LD2: high pressure Process low density polyethylene, density 0.918 g / cm ³ , MFR 0.3 g / 10 min LD: high pressure process low density polyethylene, density 0.921 g / cm ³ , MFR 0.4 g / 10 min VL1: ethylene-octene-1 co-weight Coalescence, density 0.885 g / cm ³ , MFR 1.0 g / 10 min

Example 1
LL1 as both surface layers and LL2 as an intermediate layer are put into three extruders, respectively, and the extrusion amount is adjusted so that the thickness ratio of each layer becomes 15/70/15, and the tube is formed from a three-layer annular die. After extruding, cooling water was applied from the periphery, and after cooling, it was folded with a pinch roll to obtain a tube-shaped unstretched original fabric.
The obtained unstretched original fabric was guided into an electron beam irradiation apparatus, and an electron beam irradiation treatment was performed at an irradiation dose of 40 kGy.
The obtained cross-linked unstretched raw material is guided into a stretching machine, the heating temperature at the stretching start point is set to 90 to 110 ° C., stretching is performed 5 times in the flow direction and the width direction, and the biaxial thickness is 9 μm. A stretched film was obtained.
Before winding up the obtained film, with a 1 mm long needle attached to the roll, 20 holes are continuously formed in the width direction at intervals of 2 mm in the center of the film and 2 mm in the flow direction at intervals of 2 mm. A film was obtained.
The obtained porous film was a film that was not broken at the time of perforation processing, and was able to open a hole with an appropriate hole diameter, so that the hole diameter after shrink wrapping was small and the possibility of insect invasion was extremely small.

(Examples 2 to 5)
A film was obtained in the same manner as in Example 1 except that the layer configuration was changed to the configuration shown in Table 1. Since the obtained film was not broken during the drilling process and was able to open a hole with an appropriate hole diameter, the maximum hole diameter after shrink wrapping was 500 μm or less, and there was very little possibility of insect invasion. It was a film.

(Example 6)
A porous film was obtained in the same manner as in Example 1 except that through-holes were provided at intervals of 2 mm in the width direction and at intervals of 2 mm in the flow direction at the intersections of the cuts under the following conditions.
As the cutting conditions, the angle between the cut A and the tear propagation direction is 45 °, the distance between the adjacent cuts A is 1.4 mm, the angle between the cut B and the tear propagation direction is −45 °, and the distance between the adjacent cuts B. Was 1.4 mm, and the tear propagation direction of the obtained film was the TD direction.

(Comparative Example 1)
A film was obtained in the same manner as in Example 1 except that the layer configuration and production conditions were changed as shown in Table 1. The surface of the film obtained is less rough, and when the needle is pierced into the film, the film is easily scratched, and there are those in which the pore diameter exceeds 0.8 mm, and the pore diameter after shrink wrapping exceeds 500 μm. It was a film with a high possibility of insects invading.

(Comparative Example 2)
A film was obtained in the same manner as in Example 1 except that the layer configuration and production conditions were changed as shown in Table 1. The surface of the obtained film was greatly roughened. In particular, the haze after heat shrinkage (after packaging) exceeded 3.0, and the transparency was lowered.

  The polyethylene-based crosslinked shrink film of the present embodiment relates to a perforated film having a through-hole that is brought into close contact with and shrinks by the heat shrinkage. In particular, it is suitable for packaging an item to be packaged that is reheated in a microwave oven after packaging a lunch box container or a side dish container.

1 Film 2 Cut A
3 Cut B
4 Through-hole TTD Tensile propagation direction MD Flow direction TD Width direction DD1 Perpendicular direction DD2 with respect to cut A DD Perpendicular direction with respect to cut B Q1 Spacing of adjacent cut B Q2 Spacing of adjacent cut A φ1 Tensile propagation direction and cut A The angle between the direction of tension propagation and the notch B

Claims (5)

Including at least one polyethylene film layer;
A polyethylene-based crosslinked shrink film having a root mean square height (Rq) of at least one surface of 10.0 to 50.0 nm and having a through-hole, which is measured by a white laser interferometer.   The polyethylene-based crosslinked film according to claim 1, wherein the through hole has a hole diameter of 1 to 500 μm. Polyethylene crosslinked shrink film according to the through hole to chromatic ² 100-3000 per 10cm to claim 1 or 2.   A lunch box / prepared food package packaged with the polyethylene-based crosslinked shrink film according to any one of claims 1 to 3.   A cut vegetable package packaged with the polyethylene-based crosslinked shrink film according to any one of claims 1 to 3.

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